Spider silk, which has been evolving for over 450 million years, has a tensile strength greater than steel and elasticity greater than nylon. A number of spider silk genes have been cloned and sequenced revealing specific amino acid motifs that have been conserved for over 125 million years. The key element in taking the next step toward generating biobased materials from spider silks will be to move from the current descriptive data to predictive knowledge. No one has systematically varied the sequence motifs in the spider silk proteins and determined how this influences the mechanical properties of the resulting fibers. These experiments will provide the predictive knowledge enabling the design of materials with very specific elastic and strength properties for each different medical application. This proposal is designed to test three basic hypotheses and engineering concepts. 1) Amino acid sequence motifs from spider silk assembled into a protein can be used to create self-assembling elastic materials. 2) The elasticity of the materials will be proportional to the number of elastic motifs. 3) Varying the sequence of the elastic regions will vary elastic (Young's) modulus. A brief work plan is described here. 1) Genes will be constructed with variations in the number and sequence of elastic motifs, based on naturally occurring spider silk sequences and the encoded proteins expressed in a suitable host system, 2) Each of these different proteins will be used to make both fibers and thin films. 3) The films and fibers will be tested for their mechanical properties. The properties to be measured will be tensile strength, elasticity (recoverable elongation), total elongation, energy to break and elastic modulus, 4) The structure of the protein in solution, films and fibers will be determined by Fourier transform infrared spectroscopy (FTIR) and circular dichroism (CD) and by solid state NMR. 5) The elasticity and elastic modulus data will be correlated with the number and sequence of each type of motif to produce a prediction algorithm for elastic and other materials properties. This project is highly significant for several reasons. First it will provide a basic understanding of elasticity and tensile strength in spider silk proteins, Specifically, it will reveal what controls the amount of elasticity and elastic modulus and if these two factors can be varied in a predictable way. Second this project will advance our ability to use spider silk as a biomaterial. If our hypotheses are correct we will learn how to control the elasticity and other materials properties by controlling the protein sequence. Possible applications of spider silk range from artificial ligaments and tendons to bandages for burns to composite materials for multiple applications.